Microbiological synthesis of L(+)-lactate is based on homolactic fermentation, resulting in two molecules of lactate from one molecule of hexose fermented (for example glucose or galactose).
Industrial chemical synthesis of pure L(+)-lactate is not resolved up to know, therefore there is no alternative to the microbiological synthesis of this compound.
In microbiological synthesis of L(+)-lactate, from the point of view of efficiency of energy consumption the maximum possible cultivation temperature of the microbial strain favouring set up the fermentation process without a high temperature sterilization steps of equipment and fermentation media is crucial.
In currently available processes based on Lactobacillus species the cultivation temperature does not exceed 45° C. that does not exclude contamination with thermophilic microorganisms if cultivation proceeds in rich nutrient media in nonsterile conditions. (J. H. Litchfield; In Advances in Applied Microbiology, Neidleman S. L. ed, Vol. 42, pp 45–95, 1996). The optimal cultivation temperature is 52° C. in processes based on Bacillus coagulans TB/04 (T. Payot, Z.Chemaly, F. Fick Enzyme and Microbial Technology, 24, pp 191–199). The disadvantage in this case is inhibition of the process at high concentrations of sugars (over 7,5%) complicating the use of this strain in industrial scale.
The prototype to the present invention is the microbial strain Bacillus coagulans DSM 5196. (U.S. Pat. No. 5,079,164; C12P 7/56, C12R 1/07; Jungbunzlauer Aktiengesellschaft, 1992). In the processes based on this organism the optimum cultivation temperature is 52° C. It is possible to cultivate this organism at the initial concentration of sugars up to 20%. However, this organism can convert only 70% of glucose or sucrose of the growth media to lactate that is less than in current industrial applications (85–90%).
Furthermore, Bacillus coagulans DSM 5196 is not able to hydrolyse starch, dictating the need of preliminary treatment of the starch as a cheep raw material (liquefaction and saccharification) in the separate technological process.